BD, manic-depressive illness is a severe, chronic and disabling disorder with a life-time prevalence of 1.2 percent. The discovery of lithium's efficacy as a mood-stabilizing agent revolutionized the treatment of patients with BD, but, despite its role as one of psychiatry's most important treatments the biochemical basis for lithium's antimanic and mood-stabilizing actions remains to be fully elucidated. Elucidation of the mechanism(s) by which lithium stabilizes an underlying dysregulation of limbic and limbic-associated function also offers the potential to delineate the underlying etiology/pathophysiology of BD. A major problem inherent in neuropharmacologic research, however, is the difficulty in attributing therapeutic relevance to any observed biochemical finding. One potential approach to ascribe therapeutic relevance to any biochemical findings is to identify common biochemical targets which are modified by drugs belonging to the same therapeutic class but possessing distinct chemical structures (e.g., lithium and valproic acid (VPA)). A large body of data has shown that lithium exerts major effects on the PKC signaling pathway. Most of the data, however, has been derived from preclinical rodent studies, thereby precluding an adequate understanding of the therapeutic relevance of these biochemical findings. These studies indicate two important and highly clinically relevant directions for future research: first, it is important to determine if similar modulation of the PKC signaling pathway is also brought about by other pharmacological agents with proven efficacy in the treatment of BD such as VPA; and second, it is critical to ultimately elucidate the relationship between these biochemical changes and clinical response, which may lead to the identification of biochemical and/or genetic predictors of outcome. Thus, in this proposal, the investigator's specific aims are to: 1) Characterize the effects of VPA on the PKC signaling pathway in the brain. In order to ascribe potential therapeutic relevance to the biochemical findings, they will be investigated in parallel with lithium: a) in specific brain regions, and b) in a clinically meaningful temporal profile, namely acutely, chronically, following medication withdrawal, and medication re-administration. 2) Determine the relationship between the lithium or VPA-induced changes in the PKC signaling system in rat brain and in rat peripheral cells; ultimately the investigator wishes to determine the relationship between treatment-induced changes in the PKC signaling system and treatment response in BD patients. The demonstration of a relationship between the changes in the CNS and the periphery in rodents will allow for a subsequent investigation in BD patients. This is imperative because, in order to establish therapeutic relevance for any biochemical findings, it is necessary to demonstrate: a) that these biochemical effects do, in fact, occur in patients administered the pharmacological agents in a clinically relevant paradigm; and b) that there is a relationship between the biochemical changes and treatment response. Ultimately, elucidating the mechanisms by which lithium and VPA stabilize mood should improve the prospects for the development of more effective long-term treatments, and for the identification of biochemical predictors of treatment response.